This invention relates to communications systems in general and more particularly to a communication system employing optical fibers as transmission elements.
Extreme advances have been made in the development of fiber optic communication systems. At the present state of technology, there are a great number of commercial applications of such systems and it has been indicated that fiber optics will be extensively employed in regard to communications systems such as telephone, data processing and so on.
The fiber optic has extreme advantages over twisted pair wire systems and coaxial cable systems. With the advances made in technology, industry anticipates that graded-index fibers with under 5 db loss and operating at bandwidths greater than 500 MHz will be relatively inexpensive and will be completely compatible with the costs of cable copper wire. In general, the optical fiber is expected to be economically superior to wire or cable communications as the fiber offers large bandwidths, small size and decreased weight. It is further known that optical fiber cable is easier to install and generally easier to assemble.
In any event, there is a great need in any communication system to achieve high reliability and thus to achieve optimum operation for both undersea and overland transmission of information. Coaxial cable systems as presently used are associated with high reliability. To achieve high reliability in coaxial systems, the number of repeaters and the number of active parts in each repeater are minimized. Also, each part used is specially developed, selected and tested to demanding specifications. Such procedures have developed in the coaxial cable art over an extensive period and present techniques are still time consuming and expensive. For optical fiber systems, reducing the number of parts in a transmission system is even more difficult due to the required high gain and complexity. One reason that optical fiber repeaters may be more complex than their coaxial counterparts is that conventional fault location techniques will not operate in an optical fiber system. In coaxial systems including telephone transmission systems, the art of fault location is relatively sophisticated but such approaches have no applicability and hence, cannot be employed with optical fibers.
It is therefore an object of the present invention to provide an improved transmission or communication system employing optical fibers. The transmission system employs redundant elements for achieving automatic fault control and high reliability. Based on the use of redundant optical components, one can achieve large improvements in reliability while using relatively conventional components, as well as fault location.